Heating method and apparatus



July 12, 1960 Filed Jan. 23, 1956 5 Sheets-Sheet 1 iymn- Tull- IN V EN T0R.

J.D. NESBITT BY T. W. MUNFORD AT ORN Y July 12, 1960 J NEsBlTT ETAL 2,944,805

HEATING METHOD 'AND APPARATUS 5 Sheets-Sheet 2 Filed Jan. 23, 1956 INVENTORJ VI Tm m I. F T BN H U E N D w J T wwa/ y 1960 J. D. NESBITT L HEATING METHOD AND APPARATUS 5 Sheet's-Sheet 3 Filed Jan. 23, 1956 INVENTOR.

J.D. NESBITT BY T.W.MUNFORD dm/za AT RNE u I July 12, 1960 NE B 'T HAL 2,944,805

HEATING METHOD AND APPARATUS 5 Sheets-Sheet 4 m m J 4- m m6 1 9 1 INVENTOR.

J.D. NESBITT BY T.W. MUNFORD ATTO ET will besubsequenily explained.

Un d swwslaten "i 1 2,944,805 HEATING METHOD AND APPARATUS john D. Nesbitt, Sylvania, and Theodore W. Munford,

Toledo, Ohio, assignors, by nesne assignments, to Midland-Ross Corporation,'Clevelamh'Qhio, a corporation 'ofOhio. a v Filed was. 23, 1956,: Ser. No. 560,479 lz ciaims. ci. 263-4 This invention relatesftoanimproved method of heat ing work and to apparatus therefor. f v

The invention has particular application'jin the non-' ferrous metal industryli pecially. for the heating of-billets;

for extrusion andgforging, butfis applicable to {heating any metals ,whichare subject to variation in emissivity, as

; Heating tojfo'rging, temperatures of non-ferrous metals such iasbrass, alurhiriumbr copper'prior to forging is generally accomplished in batch-type,'slot furnaces. These furnaces, which are well known in the art, consist of rec-I tangulan'direct fired combustionchamber having openf slots-fthrough which the billetsto be heated are charged; An operator grasps a tray containing, the work with a pair of tongs, and passes it through the slot, onto the hearth. Here'it is allowed to remain until a visual in spection indicates .the work is' at proper forging tempera-- ture, whereupon the tray'and work are removed, and the workis-then'forged, Temperature uniformity is rare in these cases, the average-temperature ofthe work being other hand,texhibited large variations in temperature from piece to-piece', and for this reason unsatisfactory results were obtained.

Heat transferred to the work by radiation is dependent upon the emissivity of the work. Emissivity is a factor of both the quality or characteristics of the surface and also of the color of the material, and a difference in emissivity of adjacent work pieces will thereby produce a substantial temperature differential in these pieces. For instance, theoretically a difference in emissivity of .005 between two pieces will make a variation in finalwork temperature of 70 F. or more in rapid heating to about 1450 F; In a test, two brass billets were heated to 1450 F. by a slot burner of the type shown in patent to Nesbitt and Schramm 2,591,283. 7 The billets were previously pickled to-obtain as'nearly equal emissivity as' possible. Varileft to the judgment of the operator, and this method of heating also tendsto scale the work.

To avoid overheating the h tter pieces or' portions of pieces, lower average forging temperatures must be used andmany dies cannot be properly filled by the relativelycold work. Scale often becomes imbedded in the workv causing rejects. Flow patterns due to non-uniformity of heating become variable and undependable. 'With production of uniformly heated, clean work, the'production is increased,'uniformity and quality are improved, smaller,

less powerful forging equipment may be used and designs.

not previously forged may be easily produced. :High speed heating primarily by radiation heat has been proposed for this class of work, and has been applied to the heating of largetbillets, generally 6 inches;

transfer diameter 'or more, as illustrated in our co-pending applica;

tion SLN. 353,592, now United States Patent 2,802,657,"-

issued August 13,- 1957. The work is rapidly heated and brought to temperature by this method and produces a:- product relatively 'freeIfrom scalezand zinc blush because:

of the short period oftirneit isin the furnace. Y Temperaa contact thermocouple, a

device not useable inthe case of smaller pieces." f a and zinc-blush because of the short period of time it was in the furnace.

ture differences from piece to piece-are sometimes avoided;

. by actuallymeasuringdischargeqwork temperatures with e J a 4 Figure 6 'lSIaI1fil6V3IlQll view oftheeharge mechanism To obtain high production rates n treat ng small billets I v t with reasonably sized equipment and without excessive scaling or zinc blush, high thermal head, radiation furnaces were tested in the non-ferrous industryfor heatingbrass billets. Heat was transmitted primarily by; radiation to work which was passed through the chamber. 7 The work I a was rapidly heated and brought to temperature by this 7 method,;and was produced relatively free from scale between adjacent pieces; but non-ferrous metals, on the Figure l is a cross see a of. Figure 8,

differential found ranged from 40 F. to 200 F. This occurred in spite of the-factuthat pieces were alternated in their positions to obtain as similar conditions as' possible. Another experiment was conducted with different pairsv of brass billets,"one being bright and the other black,

which wereheated principally by radiation in a mume furnace. The temperature differential occurring here was 400 F. as a maximum which was an indication of approximately the maximum temperature diiferential obtainable with pieces having maximum emissivity differences when heated by radiation.

It is apparent from the above that when small temper-v ature variations in work subject to emissivity variations are to be maintained, radiation heating is unsatisfactory;

Accordingly, a method of heating and apparatus therefor have been developed capable of rapidly and uniformly heating such work and utilizing a rotary hearth furnace Figure 5 is a planiview of charge mechanism used with T the furnace ofFigure 1 7 of Figure 5, P K V V p Figure.7 is a cross sectional view. online 7--7 of Figure6,:'

Figure 8 is a plan view of an index mechanism for th e furnace of Figure '1,

Figure 9 is .an elevation view of the index mechanism Figure 10 is an end view Figure 1 his a detailed view of .the locking mechanism shown on the furnace of Figure,1,1and

Figure l2' is a schematic diagram of a controlsystem' utilized with the furnace;

Patented July 12, 1960 e 'onal, elevation view on lines 1 1 10f FiguresiZ and 3 of a furnace embodying the inv'ention,

of the mechanism of Figure 9, i

andlocked'by a lock mechanism 27. This hearth is s'upp'orted'by rollers 28 which contact an annular ring 30 attached to supporting plate 31. Upon plate 31 is a layer of insulating refractory 32, hard brick 33 and 34, and castablerefractory 35 which forms the surface of the hearth and is sloped toward the central discharge hole 36 to facilitate discharging and to allow any slag residue to flow out through this hole. Castable refractory 35 contains radial grooves 37 which extend radially outward from discharge hole 36 andare reinforced by alloy members 38. These grooves allow the work, which may be in the form of billets 40, to be maintained in proper alignment when being pushed from the hearth into the.

discharge hole. The grooves also maintain the billets in proper position for being heated by high velocity and high temperature convection gases as will be subsequently explained.

The central discharge hole 36 has a suitable metal chute 41 located therebelow for directing the discharged work to a receptacle or conveyor by means of which the billets may be conveniently transported to an area containing the forges. In place of the receptacle or conveyor, a quench tank may be installed or a holding chamber. The latter consists of a refractory lined heated chamber for holding the billets at the desired temperatureuntil ready for forging or Whatever next operation may be involved. Chute 41 is supported by appropriate members 42 which are, in turn, upheld by a fabricated supporting base 4'3. An annular seal 44 is also supported by members 42 and is located at the inner periphery of hearth 22. A cylindrical flange 45 extends from the hearth into liquid 46 forming a gas tight connection with the discharge chute. A second seal 47 is located at the outer periphery of the hearth which rotates therewith, and a second cylindrical flange 48 depends from wall 24 into liquid 49 to form a gas tight connection between the rotating hearth and stationary wall.

A cylindrical combustion chamber 59 is centrally located above the chamber 23. Five burners 51 are located on the periphery of this chamber and fire tangentially thereinto. They comprise a gas pipe 52, an annular air passage 53, and a discharge port 54 formed in refractory 55. An air manifold 56 supplies air for combustion to the air passage 53. Opening 57 is included for the inser-' tion of a suitable pilot for igniting the combustible mixtures from the burners. It may be noted here that the heating and combustion chambers are made in easily detachable sections as shown to facilitate accessibility and repair.

A steam inlet 58 is provided for emitting steam to the mixture in the central portion of chamber 56', the mixture being substantially burned by the time it reaches the center. The steam is an important factorin the operation of the furnace since it cools the temperatureof the flue gases to a desired point for heating the work, the'temperature being measured by means of a thermocouple located in passage 65 provided therefor. The steam has a second function in producing an inert atmosphere for the work to prevent scaling thereof. The effectiveness of this has been proved in actual operation where excess air has been added to chamber 549 to the point Where the gases exiting from the furnace had more than 7% free oxygen. Little scale was formed on the work even with this extreme degree of excess oxygen.

The flue gases, resulting from substantially complete combustion of the air-fuel mixture in chamber 50, and steam travel down duct 61 formed by refractory 55 and an alloy metal tube 62 into a cylindrical manifold 63. A

portion of thismanifold is cut-out over the charge-discharge groove to allow ample clearance for 'work' enter- 4 travel radially outward through pipes 64 and emit vertically downward through nozzles 65 at high velocities where they contact and heat the work, such as billets 40. The size of the nozzles will vary with the volume of mixture and steam used and also with the number of nozzles employed. Furthermore, the nozzles may be [drilled through a bar 69 (Figure 4) attachedv to radial pipe 64.. a or directly through the pipes themselves.

The number of nozzles will depend principally on the size of the work, a sutfieient number to afford uniformity in heating being requisite. The gases then exit through flues 66 of which six are equally spaced around the furnace chamber. The

a number and size of the flues actually depend on the pressure and volume of combustion products and steam emitted to the furnace chamber. The total amount of flue area must be proper to allow the mixture tobe discharged at a temperature substantially equal to the final temperature desired'for the work so that the walls of the furnace chamber will be heated to substantiallythe same temperature by these gases. Substantially no heat will then be transmittedfrom the walls by radiation to the,

except the charge-discharge groove which is in line with the charge mechanism.

The pipes 64 are close to the work and contain the high temperature convection gases. Under these conditions the radiation heating from the pipes to the work may be expected to be substantial. This heat transfer is actually small however since the projected area of the pipe is less than 30% of the total area the work sees, in most case. Furthermore, the pipes are exposed to the large areas of the walls and hearth of the chamber which are colder than the pipes and which constantly absorb heat therefrom. This maintains the outer surfaces of the pipes at least two hundred degrees cooler than the gases they contain and further decreases the radiation efieot of the pipes on the work.

Referring to Figures 5, 6, and 7, pusher 25 essentially consists of a pneumatic pusher cylinder 71, a rod 72, a tray 73 connected thereto, and suitable supporting members 74 and 75. Rollers 76 support the tray 73 and align it with a Water cooled charge opening 70 and the hearth groove work thereon. butt against the heat treated work and discharge it down the central opening as the tray advances. This eliminates the problem of the work being charged having to butt against, and discharge, the treated work as would be necessary if no tray were used. With no tray, the number of pieces pushed by the charging mechanism would be doubled with the possibility of jamming or buckling like wise increased and, depending on the length, as many as four or five billets may be contained in a groove.

When tray 73'is at the extremity of its travel and begins to retract, the stripper bar .77 is lowered to strip the billets from the tray, being prevented from retracting with it by the bar. This stripper bar is pivotally supported bya member 7 8 attached to an extension of member 75, and end of the bar is vertically moved by a passed therethrough, entering at end 84. This water exits pipe 35 at end 35 and flows back through the annular space formed between the inner Wall of bar 77 and pipe 83 and is disposed of by means of a drain pipe connected to outlet 86.

For rotating and indexing hearth 22, another pneumatic cylinder 91of Figures 8, 9 and 10 provides the Cylinder rod 92 horizontally moves a latch as power.

The front of the tray will then s v of a-plate 94 to which a latch sembly 93'which consists v 96 and depressably held in its 95 is pivotally attached at outer position by a spring 97, support 98, and rod 100.. I

A ball joint isprovided by ball 101 locatedfbetween spring 97 and a hole 102 in support 98 to allow rod 100 to freely pivot as latch 95 moves. These foregoing items are omitted from Figure 9 for clarity of illustration. Plate 94 is slideably mounted on a rail 103 to properly guide the assembly 93 in its movement. Latch 95 engages a lug 680m the under side of the hearth when rod 92 is moved outward, thus rotating the hearth. There is one lug for each groove in the hearth and so positioned to move a new groove in front of the charge opening 70 and under each radial pipe 64 upon each forward motion of rod 92. When the rod retracts, latch 95 is' pushed downward by the next lug and springs out again after passing this lug to thus be in position-for gripping on the next forward motion. A stop 104 limits this outward motion of latch 95 and maintains it in the proper posi-E tion.

consists of an. L-shaped member 112-having a grooved head 113 for engaging a lug 6 8. Member 112 is pivoted at 114 to a support 115 and is moved by a pneumatic lock cylinder 111 and rod 116 which is pivoted to a lever.

117 that is aflixed to member 112; After the hearth indexed to a new position, rod 116 is raised forcingmemf her 112 forward so that the groove in head 113 engages a lug 68 and thereby maintains the hearth in a fixed position until ready to be indexed again.

i In the operation of this mech m, the work tobe.

charged, which may consist of one longer billet orsev eral shorter ones, is placed on the charging tray which is then extended into the furnace. The stripper bar is lowered and the tray retracted, leaving the billetspositioned on the hearth which is then indexed, locked, 'and' the process repeated. Each groove, when. indexed, is positioned under a new row of nozzles enabling the billets to be constantly subjected to a high velocity stream of hot gases except during the period of time in which the hearth is actually being indexed.

The invention comprises a cylindrical heating chamber whose axis is substantially vertical'and a horiztontally disposed frusto-conical shaped hearthin the chamber and.

with its smaller end'below the larger end. An axially located discharge hole communicates. with the lower end.

of the hearth. A plurality of equally spaced radial grooves extend outwardly from the discharge hole '[OIhfi outer periphery of the hearth. There isa.v cylindrical combustion chamber axially aligned with the 1heating- To securely position the hearth after indexing, a ing mechanism 27 is included (Figures 1 and 11);; This.'

senses.

Finally, the work is withdrawn from the chamber when the temperature of it attains that desired.

The subject heating system is partlcularly advantageous for heating operations involving work temperatures between -800 and 2.000" F. Below the former temperature, heat transfer by radiation is of little importance, and conventional heating systems may be employed with good results. The latter temperature is at present an upper limitation due to the melting points of alloys available for forming the duct work for the convection gases;

dependenton the velocity .of the hot gas, being greater.

at higher velocities. Thus, a greater portion of. thevthermal load is transferred by the high velocity-gases when they impinge onthe'work than whenthe cooler;

. low velocity gases later contact the walls ofthe chamberi by 'radiatlon, at least 70% of theheat being transferred fto' the billets by convection. "Of course the percent of radiation heating will be greater for the cooler billets in the The walls of. the furnace are-therebyheated to an average" temperature less than that of these gases'and' to. an average temperature approximately equal to that of the billets. The temperatures'ofthework andrwallsbeingsubstantially equal, little heat is transmitted to thefwork charge section of the furnace and less for the hotter ones, with the. aforementioned figure of at least 70% being an average one. Depending on the factors in eachcase, this figure maybe as high as 85%. Heating by convection does not depend on emissivity of the billets and, in spite of differences in surface characteristics and color, they are, heated to uniform temperatures varying less. than. plus or minus 9 F. This is the first time known that high speed heating has been accomplished for other mate rial than steel with such a high degree of uniformity. In a specific heat treating operation, brass billets,

: measuring 1.625" in diameter and 5.625 in length and weighing 3.64% were heated to a forging temperature of 1450 F., two billets per groove. The burners for this were supplied 2,200 c.f.h. of naturalgas and approxi-f matelyten times this amount of air for combustion. Ap-- proximately l000.1bs.; per hour of '50 p.s.i. steam were i added to the combusted air-gas mixture which resulted in -a 51840" Fftemperature for the combination. ,The

"nozzles-for directing the mixture toward the work were chamber and located above it. 1 Associated withthe corn-.

bustion chamber are burner means for tangentially emitting a combustible mixture to it and an ignition meansfor igniting the mixture. A manifold is, centrally located in the heating chamber and is connected to the lowerend of the combustion chamber by means of a vertical duct.= ;;A plurality of radial pipes extend from the manifold that are each parallel with the hearthand vertically with'a groove. Each'pipefalso contains aplurality of nozzles for directing the mixture toward work in the grooves. r 4

The invention also comprises a novel heatingimethod including placing the work on the hearth of a refractory lined chamber, supplyinga mixture of; fuel and air to a combustion chamber located externally from the refractory lined chamber, burning the mixture in the combusaligned V sized in thiscase toafiordan equivalent cold velocity-of 8000 f.p.-m. Thefurnace, containing l8 radial grooves, was loaded and indexed on a 2.0 second cycle which brought the work to temperatureat a rate of 3.7 minutes 11" of thickness. and produced approximately 1300; I

per inc lbsQpfe'rhour-withinpms or minus 9 F.

For this operation in the latter portion of the furnace,

a heat coefiicient of convection, h ofapproximately 3O 7 V was attained with a heat coefiicient of radiation, h of approximately 6. Of the total heat transfer there, about tion chamber, and directing'a high velocity stream of the mixture toward the work. The stream impinges at'high velocity on the work only and subsequently contacts the surrounding hearth and walls of the chamber at low velocity. Thereby, the stream transfers the majority of its heat load to the work and then heats the walls and hearth of'the chamber to a temperature substantially equal to the final temperature desired for thevvork.

83% was accomplishedby convection. The h for any case can be increased by increasing the velocity of gases impinging the work'or'increasing the temperature or heat.-

head thereof. The larger velocity of gases or higher temperature of them will raise the temperature of the ducts and walls also, which will increase the h but not to the extent that the h r is increased. The resulting proportional increasein the heat transferred by convection 'will create an even greater temperature uniformity in the work theoretical heat transfer by convection of creatingatheoretical temperature differential, between" adjacent work'of 0 F. Thus, the temperature and velocr. ity of the gases dependfin part on the temperature uni-- formity desired as well as on the final temperature of the be accomplished in a minimum of time.

work desired. In actual practice, a heat head of the gases of at least 100F. and a ratio of h to h of at least 2 to I are necessary to maintain reasonable tolerances underany conditions.

Billets heated by this method are capable of being forged to more intricate shapes than by previous heating methods since, with. the uniformity attained, the billets may be heated to a higher temperature, closer to the melting point, without danger of any particular billet overheating and melting within the furnace. The amount of scale formation has also been decreased from that produced with previous methods. Less scale decreases rejected work due to better surfaces and increases the life of the dies. Results have shown that brass billets heat treated by this method produce stronger forgings for the same cross section.

Since billets are heated rapidly by this method, the time being less than three minutes for smaller work, the charging, stripping, indexing, and locking operations must Accordingly, a control circuit as schematically shown in Figure 12 has been developed for this mechanism which operates as follows:

-Air is supplied from air manifold 139 indirectly to pneumatic pusher cylinder 71, stripper cylinder 88, index cylinder 91, and lock cylinder 111. The cylinder rods are shown in their initial positions as the cycle begins with no indexing air being supplied to their four-way valves. Solenoid operated valve 13-1 is opened temporan'ly by means of a timer 132 to supply air to a commercially available, four-way, air operated valve 133 through line 134. This air pressure on valve 133 diverts air supplied through line 135 from line 136 to line 137 and forces push rod 72 forward, extending work into the furnace chamber. As rod 72 moves forward, air from the inactive end of the cylinder bleeds through line 138. Valves M0, M1, and 142 are operated by tangs 143 located on rod 72. As this rod moves forward, valve 149 closes and when rod 72 reaches the end of its stroke, valve 141 opens. The latter emits air from manifold 136 through lines 144 and 145 to four-way valve 146, similar to valve 133, and diverts air flow through line 147 from line 148 to line b. This air causes push rod 87 to retract and lower the stripper bar. Air from the inactive end of cylinder 80 escapes through line 151.

iAs push rod 72 reaches the end of its stroke, it also actuates valve 142 which is opened and allows air from 11115134 to bleed off. Four-way valve 13-3 then again directs air from line 135 back to line 136 and rod 7 2 retracts. Push rod87 acts quickly in bringing the stripper bar into position. The bar is thus positioned in time to strip the work off the loading tray in spite of the fact it is actuated at the same time push rod 72 begins to retract. When rod 72 again retracts to its initial position,- tang i413 opens valve 140 bleeding air from line 145. Four-way valve 146 thus allows air from line 147 to flow again through line 148 and extends rod 87 to its original position.

At the same time air is emitted to the stripper cylinder 80', it is also emitted through line 14-4 and 152 to fourway valve 153 Air supplied through line 154 is then diverted from line 155 to line 156 which retracts index push rod 92. During movement of this rod, air in the opposite end of the cylinder is bled through line .157. The push rod 92 contains a tang 168 which, as the rod retracts, moves oil of valve 17% and closes it. When push rod 92 is fully retracted, tang 163 opens the valve 171 which emits air from line 152i to line 166 and fourway valve @611. Air from line 162 is then changed from line 163 to line 164 and retracts locking push rod 116. During movement of rod 116, air in the inactive end of cylinder 111 is bled through line 165. As rod 1315 retracts, it moves off of electric limit switch 166 which causes solenoid valve 157 to open. from line 152, and the rod 92 is again extended.

Air is thus released As rod 92 moves forward; it shuts off air from line 158 by means of valve 171 and when it reaches its forward position, having indexed the hearth, it opensvalve 1:70.- This rel'easesair on four-way-valve 161 and allows air from line 162- toagain pass through line-163, thus projecting rod 116 which locks the furnace and: actuates limit switch 166' again. Limit switch 166 then closes bleed valve 167 which prevents rod, 92 from forward movement and thus the possibility of indexing the hearth, as long as rod 116 is extended to its forward position. The cycle is thus completed and the various rods are again in their initial positions until valve 131 is opened once more and another cycle commenced. A check valve 172. is located in line 152 to prevent indexing air in this line from bleeding through valve when rod 72. is retracted. This makes the operation of the index: ing valve dependent on the locking cylinder only.

The entire cycle is capable ot'rast operation since var: ious movements are accomplished simultaneously. In actual practice, cycles of less than ten seconds have been accomplished. Tosummarize the operation: The loading tray is moved into the furnace carrying with it a new charge of work, and at the same time the end of the tray pushes previous work into the central discharge opening' Upon reaching its extended position, the tray immediate- 1y begins to. retract, and at the same time the stripper bar is lowered. Also, as the loading tray is retracted, the indexing rod is retracted to its inward position. When the loading tray has been retracted, the stripper bar is immediately raised; simultaneously, the indexing rod is extended to its forward position, the locking rod retracting at the beginning of this forward movement. Upon the complete extension of the indexing rod the locking rod is again extended to lock the furnace and complete the cycle.

The foregoing discloses the best mode known to the inventors of carrying out the invention, the scope of which is limited only by the appended claims.

We claim:

1. Apparatus for heating work comprising: a heating chamber having a work supporting area on which the work is to be heated; a combustion chamber located externally to said heat treating chamber; burner means for supplying a combustible mixture of air and fuel to said combustion chamber; ignition means for igniting said mixture; duct means for carrying said mixture from said combustion chamber to said heating chamber; a plurality of pipes extending from said duct means to said work supporting area in said heating chamber said pipes being of sufficiently small diameter whereby their projected area is less than 30% of the total area the work is exposed to, the remaining area'comprising the walls and hearth ofsaid heating chamber; and a plurality of nozzles in each of said pipes for directing said mixture toward said work supporting area, said nozzles being sufliciently close to the work supporting area to assure that all of the mixture emitting from said nozzles will directly impinge on said work.

2. Apparatus for heating work by convection comprising a cylindrical combustion chamber; a work heating chamber; burner means for emitting a combustible mixture tangentially to said combustion chamber; ignition means for i niting said mixture, an inlet axially located at one end of said combustion chamber, steam supply means for emitting steam to said inlet, and duct means for directing the combusted mixture and steam from said chamber to work in said work heating chamber.

3. The combination according to claim 2 wherein said duct means comprises an axially aligned passage connecting the end of said chamber, opposite the steam inlet end, to a series of radially extending pipes, said pipes containing a plurality of nozzles for emitting the combusted mixture and steam toward the work.

4. In a rotary hearth furnace having a central discharge port, a hearth, and a plurality of equally spaced grooves in the hearth extending radially from said discharge port to the outer periphery of the hearth for containing work to be heat treated, a heating system comprising: a cylindrical combustion chamber externally and axially located with respect to the axis ofthe furnace; burner means for emitting a combustible mixture sub stantially tangentially into said combustion chamber; ignition means for igniting said mixture; an inlet axially aligned with said chamber and opening into one end thereof; steam supply means for supplying steam through said inlet to the substantially combusted mixture; a manifold centrally located in the furnace and above the hearth; a duct connecting the other end of said combustion chamber to said manifold; a plurality of radial pipes extending from said manifold, each pipe being aligned with a groove in the hearth; and a plurality of nozzles in each pipe for directing said steam and said mixture from said pipes to work contained in the grooves.

5. A rotary hearth furnace comprising: a cylindrical heating chamber whose axis is substantially vertical; a horizontally. disposed frusto-conical shaped hearth located in said chamber and whose smaller end is below the larger end; an axially located discharge hole communicating with said lower end; a plurality of equally spaced, radial grooves in said hearth extending from said discharge hole to the outer periphery of said hearth; a cylindrical combustion chamber axially aligned with said heating chamber and located thereabove; burner means for tangentially emitting a combustible mixture to said combustion chamber; ignition means for igniting said mixture; a manifold centrally located in said heating chamber; a vertical duct axially aligned with saidchambers and connecting the lower end of said combustion chamber to said manifold; a plurality of radial pipes extending from said manifold, parallel to said hearth, and

each being vertically aligned with a groove; and a plurality of nozzles in each pipe for directing said mixture toward work in said grooves.

6. Charging mechanism, for loading work to be heat treated into a furnace chamber having a work receiving surface, comprising: a support; a roller supported by said support; a tray adapted to receive work, supported on said roller, initially located externally to said chamber, and parallel to said work receiving surface; a fluid operated cylinder axially aligned with said tray, said cylinder including a pushrod connected with an end of said tray to extend said tray into the furnace chamber; a stripper bar adapted to strip work from said tray after being carried into the furnace chamber; and power means for moving said bar into and out of interference with the travel of said work.

7. The apparatus according to claim 6 characterized by control means for controlling the operation of said cylinder and said power means whereby said stripper bar is moved into interference with the travel of said work after said push rod and tray are extended into said chamber to prevent retraction of the work when said rod and tray are retracted, and said bar is moved away to prevent interference with said rod and said tray when again extended.

8. The method of heating metal work to a desired temperature which comprises: placing said work in a retiree tory lined chamber; heating a gas to a temperature substantially higher than the desired final temperature for said work, said gas being substantially inert to the metal work; tempering the gas to a temperature at least 100 F. higher than the final temperature desired for said work; impinging a high velocity stream of the tempered gas upon said work; removingsaid gas-from said chamber at a temperature substantially equal to said desired temperature whereby the walls of said chamber are heated only by the gases leaving the work to a temperature substantially equal to that desired for said work and a relatively small amount of heat is transferred from said wall to said work by radiation, the heating of said work being accomplished with the coefficient of convection being at least twice the coeflicient of radiation; and discharging said chamber when its temperature attains that desired.

9. The method of heating non-ferrous metal work to a desired temperature substantially by convection at high rates of convective heat transfer comprising: placing the work on the hearth of a refractory lined chamber; heating a gas inert to said metal work in a chamber located externally to said refractory lined chamber; creating a high velocity stream of said heated gas; impinging said high velocity stream of gas upon said work at a temperature substantially higher than the final temperature desired for said work, said stream expending its velocity upon impinging said work and subsequently contacting the surrounding hearth and walls of said chamber at a low velocity whereby said stream transfers the majority of its excess heat to said work; and immediately withdrawing said work from said refractory lined chamber I when the temperature of said work reaches that desired.

10. The method according to claim 9 characterized by admitting steam to said stream before said streamis impinged upon said work.

1 1. The method of heating non-ferrous metal work to a desired temperature substantially by convection at high rates of convective heat transfer comprising: placing the work on the hearth of a refractory lined chamber; heating a gas inert to said metal work in a chamber'located externally to said refractory lined chamber; creating a high velocity stream of said heated gas; impinging said high velocity stream of gas upon said work at a tempera ture substantially higher than the final temperature desired for said work; transferring the majority of excess heat in the gas to said work; substantially decreasing the velocity of the gas immediately after it impinges said work; withdrawing said gases from said refractory lined chamber; and immediately removing said work fromsaid refractory lined chamber when the temperature of said work reaches that desired.

12. A rotary. hearth furnace for high velocity, convection heating of a plurality of work pieces comprising: a cylindrical heating chamber; a hearth for supporting said work pieces thereon whose surface is of frusto-conical configuration and whose smaller end is lower than the larger end; means forming a discharge hole communicating with said smaller end through which said work pieces and residual slag are discharged from said surface; a plurality of radial grooves in said surface extending from said discharge hole to the outer periphery of said hearth for holding the work pieces on the hearth; a manifold located in said surface above said hearth; a plurality of radial pipes extending from said manifold, each pipe adapted to be aligned above a groove in the hearth; a plurality of nozzles in each pipe; and means for supplying heated gas 

